1. Field of the Invention
The present invention provides an apparatus and methods for use in wellbores. More particularly, the invention provides an apparatus and methods for use with a cement shoe assembly having an isolation sleeve for use in monobore wells. Even more particularly, the invention provides a cement shoe assembly with an enlarged inner diameter portion and a sleeve for isolating the enlarged portion from the bore of the cement shoe, thereby facilitating the expansion of a tubular into the enlarged portion after cementing. The invention also provides an isolation sleeve for use with a casing in a monobore well.
2. Description of the Related Art
In the drilling of a hydrocarbon well, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of tubulars or casing. The casing is subsequently cemented, thereby protecting the formation and preventing the walls of the wellbore from collapsing. The casing also provides a reliable path through which drilling tools, drilling mud, and ultimately, production fluid may travel.
After the wellbore is lined with the initial string of casing, the well is drilled to a new depth. A new string of tubulars or liner is then lowered into the well. The new liner is positioned so that the top of the liner overlaps the bottom of the existing casing. Thereafter, with the liner held in place with a mechanical hanger, the liner is cemented. In cementing a tubular string, a column of cement is pumped into the tubular and forced to the bottom of the wellbore where it flows out and flows upward into an annulus defined by the wellbore and the new string of liner.
In order to facilitate cementing of a tubular string in a well, a cementing apparatus referred to as a cement shoe may be lowered into the wellbore at the bottom of the tubular string to be cemented. The shoe typically includes various components including a tapered nose portion located at the downhole end of the tubular to facilitate insertion of the shoe into the borehole. Additionally, a check valve constructed and arranged to partially seal the end of the tubular is provided. The check valve prevents entry of well fluid during run-in while permitting cement to subsequently flow outwards. The same valve or another valve or plug typically located in a baffle collar above the cementing apparatus prevents the cement from back flowing into the tubular. Components of the cementing shoe are made of fiberglass, plastic, or other drillable material. Once the cementing is completed, the shoe and any cement remaining in the casing can later be destroyed when the wellbore is drilled to a new depth.
Recently, an apparatus has been developed for expanding the diameter of a liner in a wellbore to conform to the larger diameter of a previously run casing string. FIG. 1 is an exploded view of an exemplary expansion tool 700. The expansion tool 700 has a body 702 which is hollow and generally tubular with connectors 704 and 706 for connection to other components (not shown) of a downhole assembly. The connectors 704 and 706 are of a reduced diameter compared to the outside diameter of the longitudinally central body part of the tool 700. The central body part has three recesses 714 to hold a respective roller 716. Each of the recesses 714 has parallel sides and extends radially from a radially perforated tubular core (not shown) of the tool 700. Each of the mutually identical rollers 716 is somewhat cylindrical and barreled. Each of the rollers 716 is mounted by means of an axle 718 at each end of the respective roller and the axles are mounted in slidable pistons 720. The rollers are arranged for rotation about a respective rotational axis, which is parallel to the longitudinal axis of the tool 700, and radially offset therefrom at 120-degree mutual circumferential separations around the central body. The axles 718 are formed as integral end members of the rollers 716 and the pistons 720 are radially slidable, one piston 720 being slidably sealed within each radially extended recess 714. The inner end of each piston 720 is exposed to the pressure of fluid within the hollow core of the tool 700 by way of the radial perforations in the tubular core. In this manner, pressurized fluid provided from the surface of the well, via a tubular, can actuate the pistons 720 and cause them to extend outward and to contact the inner wall of a tubular to be expanded. Additionally, at an upper and a lower end of the expansion tool 700 are a plurality of non-compliant rollers 703 constructed and arranged to initially contact and expand the tubular prior to contact between the tubular and fluid actuated rollers 716. Unlike the compliant, fluid actuated rollers 716, the non-compliant rollers 703 are supported only with bearings and they do not change their radial position with respect to the body portion of the tool 700.
Historically, each string of tubulars inserted to line a wellbore has necessarily been smaller in diameter than the string previously inserted. In this respect, the wellbore typically consists of sequential strings of tubulars of an ever-decreasing inner and outer diameter. The ability to expand a tubular in situ has led to the idea of monobore wells, wherein through the expansion of entire tubular strings in the wellbore, the wellbore remains at about the same inner diameter throughout its length. The advantages of the monobore well are obvious. The tubulars lining the borehole, and therefore, the possible path for fluid in and out of the well remains consistent regardless of well depth. Additionally, wellbore components and other devices can more easily be run into the well without regard for the restriction of decreasing diameters of the lining encountered on the way to the bottom of the wellbore. One problem with monobore wells relates to the difficulty of expanding one tubular into another when the outer tubular is cemented into the wellbore, preventing the outer diameter from increasing as the inner tubulars is expanded into it.
In order to facilitate the assembly of tubular strings to form a monobore, the lower portion of the upper string of tubulars is specifically designed with an enlarged inner diameter in the area that will receive the expanded upper portion of a lower string. To join the tubulars with an expansion means, the upper end of the second string is aligned with the enlarged inner diameter portion of the first string. An expansion tool is used to radially expand the upper end of the second string into the enlarged inner diameter portion to approximately the same inner and outer diameter as the first string. In this manner, the second tubular string is expanded into the first string without an increase in the outer diameter of the first string and without the use of conventional slips.
In an example of the above-described design, a cement shoe is built into the lower portion of the first string of tubulars. The housing of the shoe has an enlarged inner diameter portion as discussed above. After the cement shoe is used to cement the tubular string in the wellbore, the interior portions of the shoe are drilled out as a new borehole is formed therebelow. Subsequently, a second string of tubulars is run into the new section of borehole, and the upper portion of the second string of tubulars is expanded into the enlarged inner diameter portion of the first string as described herein.
Because of the enlarged inner diameter portion of the first string, subsequent drilling of the cement shoe is usually inadequate to remove some residual material from the lower portion of the string. The material typically remains around the inside wall of the enlarged inner diameter portion because the outer diameter of the drill bit does not reach it. The residual material can interfere with the connection between the upper end of the next string of tubulars and the lower end of the existing string. Additionally, the residual material may extend into the bore and interfere with wellbore components that are run-in into the wellbore.
A need, therefore, exists for an apparatus and method to more efficiently prevent the accumulation of residual material in a tubular prior to connection to another tubular by expansion. There is a further need for a cement shoe that can be used in a tubular string without leaving residual material in an enlarged inner diameter portion of the string. There is a yet a further need for a cement shoe with an enlarged inner diameter portion and a method and apparatus for temporarily isolating the enlarged inner diameter portion from residual material.
The present invention generally provides an apparatus and methods to prevent unwanted materials such as cement from accumulating in a lower portion of a tubular having an enlarged inner diameter portion. A cement shoe assembly is provided at a lower end of a tubular string with a sleeve co-axially disposed therein to cover the enlarged inner diameter portion of the tubing. The sleeve serves to temporarily make the diameter of the tubular uniform and to isolate an annular area between the outside of the sleeve and the inner wall of the casing. A method of preventing accumulation of unwanted materials by disposing a sleeve in the enlarged inner diameter portion and later expanding the sleeve into said portion is provided. In one embodiment the sleeve is dissolvable. In another embodiment, a deformable sleeve with at least one internal ring is provided to cover the enlarged inner diameter portion. In still another embodiment, the sleeve is retrievable from the surface of the well.